Seismic response of connections in indeterminate R/C frame subassemblies

Abstract

The behavior of beam-to-column connections under earthquake-type loading has been studied in the past by testing isolated interior or exterior connections. In such tests, the beams are allowed to elongate freely when subjected to large deformation reversal. In a real building, however, the beams may be partially restrained against such elongation. The current design procedures which have been developed on the basis of tests on isolated connections, therefore, ignore the effects of continuity and beam elongation on the performance of connections. In this investigation, the behavior of connections was studied by testing indeterminate frame subassemblies under earthquake-type loading. Six half-scale multiple-connection subassemblies were tested. Each subassembly consisted of a two-bay frame isolated at the column mid-heights. Five single connection subassemblies were also treated to correlate the behavior of connections in multiple-connection subassemblies with the behavior of connections observed by testing isolated connections. Tests have shown that restriction to elongation of beams in indeterminate systems resulted in axial compression in beams which in turn had a significant effect on the performance of connections. The joint shear increased in both interior and exterior connections and the column-to-beam flexural strength ratio decreased. The energy dissipation was not affected by the continuity, but the lateral load resistance increased significantly. The stiffness degradation was more controlled and gradual in the indeterminate subassemblies compared to that observed in isolated connections. Based on the observed mechanism of lateral load resistance and the observed behavior of connections, a procedure is presented to account for the presence of axial compression in the main beams in the design of beam-to-column connections